U.S. patent application number 15/522178 was filed with the patent office on 2017-11-23 for method and device for communication using unlicensed band in mobile communication system.
The applicant listed for this patent is Samsung Electronics Co., Ltd.. Invention is credited to Rayeon AHN, Jungsoo JUNG, Sungjin LEE, Jungmin MOON, Seunghoon PARK, Sunheui RYOO.
Application Number | 20170339588 15/522178 |
Document ID | / |
Family ID | 55858505 |
Filed Date | 2017-11-23 |
United States Patent
Application |
20170339588 |
Kind Code |
A1 |
MOON; Jungmin ; et
al. |
November 23, 2017 |
METHOD AND DEVICE FOR COMMUNICATION USING UNLICENSED BAND IN MOBILE
COMMUNICATION SYSTEM
Abstract
The present disclosure relates to a pre-5th-Generation (5G) or
5G communication system to be provided for supporting higher data
rates Beyond 4th-Generation (4G) communication system such as Long
Term Evolution (LTE). The present invention relates to a method by
a base station in a mobile communication system, the method
comprising the steps of: checking a channel state in an unlicensed
band; determining a parameter for checking whether a channel is
occupied, according to the channel state; and transmitting the
determined parameter to a terminal.
Inventors: |
MOON; Jungmin; (Suwon-si,
KR) ; RYOO; Sunheui; (Yongin-si, KR) ; AHN;
Rayeon; (Seoul, KR) ; LEE; Sungjin;
(Bucheon-si, KR) ; JUNG; Jungsoo; (Seongnam-si,
KR) ; PARK; Seunghoon; (Seoul, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Samsung Electronics Co., Ltd. |
Suwon-si, Gyeonggi-do |
|
KR |
|
|
Family ID: |
55858505 |
Appl. No.: |
15/522178 |
Filed: |
November 2, 2015 |
PCT Filed: |
November 2, 2015 |
PCT NO: |
PCT/KR2015/011633 |
371 Date: |
April 26, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62073379 |
Oct 31, 2014 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W 16/14 20130101;
H04W 88/02 20130101; H04W 74/0808 20130101; H04L 5/14 20130101;
H04W 24/08 20130101; H04W 72/085 20130101; H04W 72/0446 20130101;
H04W 76/27 20180201; H04W 72/042 20130101; H04W 88/08 20130101 |
International
Class: |
H04W 24/08 20090101
H04W024/08; H04L 5/14 20060101 H04L005/14; H04W 76/04 20090101
H04W076/04; H04W 72/04 20090101 H04W072/04 |
Claims
1. A communication method of a base station in a mobile
communication system, the method comprising: checking a state of a
channel in an unlicensed band; determining parameters for checking
channel occupancy according to the channel state; and transmitting
the parameters to a terminal.
2. The method of claim 1, wherein determining the parameters
comprises: determining a contention window size based on a number
of transitions from an occupancy state to an idle state, the number
of transitions being included in channel state information
generated based on the channel state; and determining a channel
occupancy check duration included in the parameters based on the
contention window size.
3. The method of claim 2, wherein the contention window size
increases when the number of transitions from the occupancy state
to the idle state increases.
4. The method of claim 1, wherein the parameters are included in at
least one of a Physical Downlink Control Channel (PDCCH), a System
Information Block (SIB), a Radio Resource Control (RRC)
configuration message, and an RRC reconfiguration message being
transmitted to the terminal.
5. A communication method of a base station in a mobile
communication system, the method comprising: determining
configuration information on subframes including downlink subframes
consecutive within a predetermined time period in an unlicensed
band; and transmitting the configuration information to a
terminal.
6. The method of claim 5, wherein the configuration information
comprises at least one of a length of the consecutive downlink
subframes, a start time point of the consecutive downlink
subframes, a length of the consecutive uplink subframes, and a
start time point of the consecutive downlink subframes.
7. The method of claim 5, wherein the configuration information is
determined based on a size of data to be transmitted.
8. The method of claim 5, wherein the configuration information is
included in at least one of a Physical Downlink Control Channel
(PDCCH), a System Information Block (SIB), a Radio Resource Control
(RRC) configuration message, and an RRC reconfiguration message
being transmitted to the terminal.
9. A base station of a mobile communication system, the base
station comprising: a transceiver which communicates with a network
entity; and a controller which checks a state of a channel in an
unlicensed band, determines parameters for checking channel
occupancy according to the channel state, and controls the
transceiver to transmit the parameters to a terminal.
10. The base station of claim 9, wherein the controller determines
a contention window size based on a number of transitions from an
occupancy state to an idle state, the number of transitions being
included in channel state information generated based on the
channel state and determines a channel occupancy check duration
included in the parameters based on the contention window size.
11. The base station of claim 10, wherein the contention window
size increases when the number of transitions from the occupancy
state to the idle state increases.
12. The base station of claim 9, wherein the parameters are
included in at least one of a Physical Downlink Control Channel
(PDCCH), a System Information Block (SIB), a Radio Resource Control
(RRC) configuration message, and an RRC reconfiguration message
being transmitted to the terminal.
13. A base station of a mobile communication system, the base
station comprising: a transceiver which communicates with a network
entity; and a controller which determines configuration information
on subframes including downlink subframes consecutive within a
predetermined time period in an unlicensed band and controls the
transceiver to transmit the configuration information to a
terminal.
14. The base station of claim 13, wherein the configuration
information comprises at least one of a length of the consecutive
downlink subframes, a start time point of the consecutive downlink
subframes, a length of the consecutive uplink subframes, and a
start time point of the consecutive downlink subframes.
15. The base station of claim 13, wherein the configuration
information is determined based on a size of data to be
transmitted.
16. The base station of claim 13, wherein the configuration
information is included in at least one of a Physical Downlink
Control Channel (PDCCH), a System Information Block (SIB), a Radio
Resource Control (RRC) configuration message, and an RRC
reconfiguration message being transmitted to the terminal.
17. A communication method of a terminal of a mobile communication
system, the terminal comprising: checking channel state in an
unlicensed band; transmitting information on the channel state to a
base station; and receiving parameters for checking channel
occupancy determined based on the channel state.
18. The method of claim 17 wherein the parameters comprise a
channel occupancy check duration which is determined based on a
contention window size, the contention window size being determined
based on a number of transitions from an occupancy state to an idle
state which is included in the channel state information.
19. The method of claim 18 wherein the contention window size
increases when the number of transitions from the occupancy state
to the idle state increases.
20. The method of claim 17, wherein the parameters are included in
at least one of a Physical Downlink Control Channel (PDCCH), a
System Information Block (SIB), a Radio Resource Control (RRC)
configuration message, and an RRC reconfiguration message.
21. A terminal of a mobile communication system, the terminal
comprising: a transceiver which communicates with a network entity;
and a controller which checks channel state in an unlicensed band
and controls the transceiver to transmit information on the channel
state to a base station and receive parameters for checking channel
occupancy determined based on the channel state from the base
station.
22. The terminal of claim 21, wherein the parameters comprise a
channel occupancy check duration which is determined based on a
contention window size, the contention window size being determined
based on a number of transitions from an occupancy state to an idle
state which is included in the channel state information.
23. The terminal of claim 22, wherein the contention window size
increases when the number of transitions from the occupancy state
to the idle state increases.
24. The terminal of claim 21, wherein the parameters are included
in at least one of a Physical Downlink Control Channel (PDCCH), a
System Information Block (SIB), a Radio Resource Control (RRC)
configuration message, and an RRC reconfiguration message.
Description
TECHNICAL FIELD
[0001] The present invention relates to a mobile communication
system and, in particular, to a communication method and apparatus
operating in an unlicensed band in the mobile communication
system.
BACKGROUND ART
[0002] To meet the demand for wireless data traffic having
increased since deployment of 4G communication systems, efforts
have been made to develop an improved 5G or pre-5G communication
system. Therefore, the 5G or pre-5G communication system is also
called a `Beyond 4G Network` or a `Post LTE System`.
[0003] The 5G communication system is considered to be implemented
in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to
accomplish higher data rates. To decrease propagation loss of the
radio waves and increase the transmission distance, the
beamforming, massive multiple-input multiple-output (MIMO), Full
Dimensional MIMO (FD-MIMO), array antenna, an analog beam forming,
large scale antenna techniques are discussed in 5G communication
systems.
[0004] In addition, in 5G communication systems, development for
system network improvement is under way based on advanced small
cells, cloud Radio Access Networks (RANs), ultra-dense networks,
device-to-device (D2D) communication, wireless backhaul, moving
network, cooperative communication, Coordinated Multi-Points
(CoMP), reception-end interference cancellation and the like.
[0005] In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and
sliding window superposition coding (SWSC) as an advanced coding
modulation (ACM), and filter bank multi carrier (FBMC),
non-orthogonal multiple access (NOMA), and sparse code multiple
access (SCMA) as an advanced access technology have been
developed.
[0006] Mobile communication systems were developed to provide
subscribers with voice communication services on the move.
Recently, mobile communication systems have evolved to the level of
supporting high speed data communication services beyond the early
voice-oriented services. However, the resource shortage and user
requirements for higher speed services are spurring evolution
towards increasingly more advanced mobile communication
systems.
[0007] As one of the next-generation mobile communication systems
to meet such requirements, standardization for a Long-Term
Evolution (LTE) system is underway in the 3.sup.rd Generation
Partnership Project (3GPP). LTE is a technology designed to provide
high speed packet-based communication of up to 100 Mbps and aims at
commercial deployment around 2010. In order to accomplish this aim,
discussions are being held on several schemes: one scheme for
reducing the number of nodes located in a communication path by
simplifying a configuration of the network, and another scheme for
maximally approximating wireless protocols to wireless
channels.
[0008] Recently, a technique called Licensed Assisted Access (LAA)
has been proposed to improve frequency utilization efficiency by
using Carrier Aggregation (CA) across licensed and unlicensed
bands.
[0009] As in LTE systems, Time Division Duplexing (TDD) is used in
an LLA system. There is therefore a need of a method for
determining a TDD frame structure and TDD configuration information
for use in the LAA system.
DISCLOSURE OF INVENTION
Technical Problem
[0010] The present invention has been conceived to solve the above
problems. The present invention proposes a method for determining a
TDD frame structure and TDD configuration information for use in an
LAA system. Also, the present invention proposes a method for
determining parameters for checking unlicensed band channel
occupancy based on channel condition.
Solution to Problem
[0011] In accordance with an aspect of the present invention, a
communication method of a base station in a mobile communication
system includes checking a state of a channel in an unlicensed
band, determining parameters for checking channel occupancy
according to the channel state, and transmitting the parameters to
a terminal.
[0012] In accordance with another aspect of the present invention,
a communication method of a base station in a mobile communication
system includes determining configuration information on subframes
including downlink subframes consecutive within a predetermined
time period in an unlicensed band and transmitting the
configuration information to a terminal.
[0013] In accordance with another aspect of the present invention,
a base station of a mobile communication system includes a
transceiver which communicates with a network entity and a
controller which checks a state of a channel in an unlicensed band,
determines parameters for checking channel occupancy according to
the channel state, and controls the transceiver to transmit the
parameters to a terminal.
[0014] In accordance with another aspect of the present invention,
a base station of a mobile communication system includes a
transceiver which communicates with a network entity and a
controller which determines configuration information on subframes
including downlink subframes consecutive within a predetermined
time period in an unlicensed band and controls the transceiver to
transmit the configuration information to a terminal.
[0015] In accordance with another aspect of the present invention,
a communication method of a terminal of a mobile communication
system includes checking a channel state in an unlicensed band,
transmitting information on the channel state to a base station,
and receiving parameters for checking channel occupancy determined
based on the channel state.
[0016] In accordance with still another aspect of the present
invention, a terminal of a mobile communication system includes a
transceiver which communicates with a network entity and a
controller which checks a channel state in an unlicensed band and
controls the transceiver to transmit information on the channel
state to a base station and receive parameters for checking channel
occupancy determined based on the channel state.
Advantageous Effects of Invention
[0017] The present invention is advantageous in terms of
facilitating TDD operations in an unlicensed band using a TDD frame
structure proposed for use in an LAA system. Also, the present
invention is advantageous in terms of increasing data processing
throughput by determining CCA parameters depending on channel
condition.
BRIEF DESCRIPTION OF DRAWINGS
[0018] FIG. 1 is a diagram illustrating the TDD configurations
specified in LTE;
[0019] FIG. 2 is a diagram illustrating a Frame Based Equipment
(FBE) operation and a Load Based Equipment (LBE) operation of an
base station according to an embodiment of the present
invention;
[0020] FIG. 3A is a diagram illustrating configurations of a TDD
frame according to an embodiment of the present invention;
[0021] FIG. 3B is a diagram illustrating configurations of a TDD
frame according to another embodiment of the present invention;
[0022] FIG. 4 is a diagram illustrating a method for performing CCA
on different types of channel according to an embodiment of the
present invention;
[0023] FIG. 5 is a diagram illustrating a situation where different
types of traffic are carried on different channels in an unlicensed
band to which an embodiment of the present invention is
applicable;
[0024] FIG. 6A is a diagram illustrating a situation of
transmitting LAA voice packets in an unlicensed band to which an
embodiment of the present invention is applicable;
[0025] FIG. 6B is a diagram illustrating a situation of
transmitting LAA data packets in an unlicensed band to which an
embodiment of the present invention is applicable;
[0026] FIG. 7A is a flowchart illustrating an LBT parameter
determination procedure according to an embodiment of the present
invention;
[0027] FIG. 7B is a flowchart illustrating a procedure for
determining LBT parameters based on a channel state according to an
embodiment of the present invention;
[0028] FIG. 7C is a flowchart illustrating a procedure for
determining LBT parameters based on a channel state according to
another embodiment of the present invention;
[0029] FIG. 7D is a flowchart illustrating a procedure for
determining LBT parameters based on a channel state according to
still another embodiment of the present invention;
[0030] FIG. 8 is a diagram for explaining channel state information
checked by an base station based on channel occupancy status
according to an embodiment of the present invention;
[0031] FIG. 9 is a flowchart illustrating a procedure for selecting
a channel to which the LBT parameter determined based on channel
states is applied according to an embodiment of the present
invention;
[0032] FIG. 10 is a diagram illustrating a procedure for sorting
channels into four channel groups according to an embodiment of the
present invention;
[0033] FIG. 11 is a diagram illustrating a method for determining
LBT parameters per channel according to an embodiment of the
present invention;
[0034] FIG. 12 is a signal flow diagram illustrating a procedure
for transmitting LBT parameters to a terminal according to an
embodiment of the present invention;
[0035] FIG. 13 is a block diagram illustrating a configuration of
an base station according to an embodiment of the present
invention; and
[0036] FIG. 14 is a block diagram illustrating a configuration of a
terminal according to an embodiment of the present invention.
MODE FOR THE INVENTION
[0037] Exemplary embodiments of the present invention are described
in detail with reference to the accompanying drawings. The same
reference numbers are used throughout the drawings to refer to the
same or like parts. Detailed descriptions of well-known functions
and structures incorporated herein may be omitted to avoid
obscuring the subject matter of the present invention.
[0038] Detailed descriptions of technical specifications well-known
in the art and unrelated directly to the present invention may be
omitted to avoid obscuring the subject matter of the present
invention. This aims to omit unnecessary description so as to make
the subject matter of the present invention clear.
[0039] For the same reason, some elements are exaggerated, omitted,
or simplified in the drawings and, in practice, the elements may
have sizes and/or shapes different from those shown in the
drawings. Throughout the drawings, the same or equivalent parts are
indicated by the same reference numbers.
[0040] Advantages and features of the present invention and methods
of accomplishing the same may be understood more readily by
reference to the following detailed description of exemplary
embodiments and the accompanying drawings. The present invention
may, however, be embodied in many different forms and should not be
construed as being limited to the exemplary embodiments set forth
herein. Rather, these exemplary embodiments are provided so that
this disclosure will be thorough and complete and will fully convey
the concept of the invention to those skilled in the art, and the
present invention will only be defined by the appended claims. Like
reference numerals refer to like elements throughout the
specification.
[0041] It will be understood that each block of the flowcharts
and/or block diagrams, and combinations of blocks in the flowcharts
and/or block diagrams, can be implemented by computer program
instructions. These computer program instructions may be provided
to a processor of a general-purpose computer, special purpose
computer, or other programmable data processing apparatus, such
that the instructions which are executed via the processor of the
computer or other programmable data processing apparatus create
means for implementing the functions/acts specified in the
flowcharts and/or block diagrams. These computer program
instructions may also be stored in a non-transitory
computer-readable memory that can direct a computer or other
programmable data processing apparatus to function in a particular
manner, such that the instructions stored in the non-transitory
computer-readable memory produce manufacture articles embedding
instruction means which implement the function/act specified in the
flowchart s and/or block diagrams. The computer program
instructions may also be loaded onto a computer or other
programmable data processing apparatus to cause a series of
operational steps to be performed on the computer or other
programmable apparatus to produce a computer implemented process
such that the instructions which are executed on the computer or
other programmable apparatus provide steps for implementing the
functions/acts specified in the flowcharts and/or block
diagrams.
[0042] Furthermore, the respective block diagrams may illustrate
parts of modules, segments, or codes including at least one or more
executable instructions for performing specific logic function(s).
Moreover, it should be noted that the functions of the blocks may
be performed in a different order in several modifications. For
example, two successive blocks may be performed substantially at
the same time or may be performed in reverse order according to
their functions.
[0043] According to various embodiments of the present disclosure,
the term "module", means, but is not limited to, a software or
hardware component, such as a Field Programmable Gate Array (FPGA)
or Application Specific Integrated Circuit (ASIC), that performs
certain tasks. A module may advantageously be configured to reside
on the addressable storage medium and configured to be executed on
one or more processors. Thus, a module may include, by way of
example, components, such as software components, object-oriented
software components, class components and task components,
processes, functions, attributes, procedures, subroutines, segments
of program code, drivers, firmware, microcode, circuitry, data,
databases, data structures, tables, arrays, and variables. The
functionality provided for in the components and modules may be
combined into fewer components and modules or further separated
into additional components and modules. In addition, the components
and modules may be implemented such that they execute one or more
CPUs in a device or a secure multimedia card.
[0044] FIG. 1 is a diagram illustrating the TDD configurations
specified in LTE.
[0045] In a TDD communication system, the downlink and uplink share
the same frequency such that downlink and uplink transmissions
alternate in the time domain. In LTE TDD, the downlink and uplink
signals are discriminated by subframe. The numbers of downlink and
uplink subframes may be determined to be equal to each other or
different from each other such that the number of downlink
subframes is greater than that of the uplink subframes or vice
versa, depending on downlink and uplink traffic loads. In LTE, a
radio frame consists of 10 subframes, and each subframe spans 1
ms.
[0046] In reference to FIG. 1, D denotes a downlink subframe, U
denotes an uplink subframe, and S denotes a special subframe with
the three fields: Downlink Pilot Time Slot (DwPTS), Guard Period
(GP), and Uplink Pilot Time Slot (UpPTS). The DwPTS can be used for
downlink control information transmission like an ordinary downlink
subframe or, if its length is long enough according to the
configuration of the special subframe, for downlink data
transmission. The GP is the interval required for
downlink-to-uplink switch, and its length is determined according
to the network configuration. The UpPTS can be used for
transmitting a terminal's Sounding Reference Signal (SRS) for
uplink channel state estimation and a terminal's Random Access
Channel (RACH).
[0047] For example, in case of TDD configuration #6, it may be
possible to transmit downlink data and control information at
subframes #0, #5, and #9 and uplink data and control information at
subframes #2, #3, #4, #7, and #8. The subframes #1 and #6
designated as special subframes can be used for control information
transmission or, depending on the case, data transmission in
downlink and SRS or RACH transmission.
[0048] Applying the TDD configurations to an LAA system may cause
problems as follows.
[0049] First, in the TDD configurations with a 5 ms switch
periodicity, the downlink subframes are not consecutive in a TDD
frame. If the downlink subframes are consecutive in the TDD frame,
the base station may use the consecutive downlink subframes
continuously after success in Clear Channel Assessment (CCA) or
extended CCA (ECCA). However, if the downlink subframes are not
consecutive in the TDD frame, the base station has to perform CCA
or ECCA before every downlink (DL) transmission. This is likely to
be a cause of increasing channel occupancy failure of the base
station in the LAA system.
[0050] Second, in the TDD configurations with a 5 ms switch
periodicity, two special subframes exist. This may cause a problem
in that Wi-Fi preoccupies the channel when the base station or
terminal does not transit any signal in the special subframes.
[0051] Third, the TDD configurations supported in the LTE system
operating in the licensed bands are configured per 10 ms. In the
LAA system operating in an unlicensed band and occupying the
channel for as long a time as for the data to transmit, it is not
necessary to configure the TDD configurations in consideration of
the fixed LTE frame size.
[0052] For this reason, the present invention proposes a method for
determining a TDD frame structure and TDD configurations for use in
an LAA system.
[0053] FIG. 2 is a diagram illustrating a Frame Based Equipment
(FBE) operation and a Load Based Equipment (LBE) operation of an
base station according to an embodiment of the present
invention.
[0054] In reference to FIG. 2, the timing diagram 210 shows a
situation where an base station or a terminal operating in the FBE
mode transmits data in an unlicensed band. The base station or
terminal in the FBE mode may perform CCA during a CCA duration 211.
The base station in the FBE mode may perform CCA over a
predetermined time duration (e.g., 20 .mu.s) before starting data
transmission.
[0055] The CCA is an operation in which the transmitter measures an
interference amount to determine whether another device currently
uses the unlicensed band. If it is determined that the interference
amount is less than a threshold value, the transmitter may perform
transmission in the unlicensed band as denoted by reference number
213. Here, the time duration in which the transmitter performs
transmission is referred to as channel occupancy duration 216.
[0056] The base station or terminal in the FBE mode may occupy the
unlicensed band for at least 1 ms and up to 10 ms after performing
the CCA once and then has to stay in the idle state 214 during a
time period of at least 5% of the channel occupancy duration 216.
This time period is referred to as idle duration 217.
[0057] Otherwise, if it is determined that the interference amount
is equal to or greater than the threshold value, the transmitter
may determine that the unlicensed band is currently occupied by
another device. In this case, the transmitter may skip transmission
and perform CCA during the next CCA duration 212.
[0058] However, in the case that, as a result of CCA, it is
determined that the unlicensed band is occupied by another device,
the transmitter cannot perform CCA during a predetermined time
period, resulting in resource waste.
[0059] The timing diagram 220 shows a situation where an base
station or terminal in the LBE mode transmits data in an unlicensed
band. Like the base station or terminal in the FBE mode, the base
station or terminal in the LBE mode has to perform CCA during the
CCA duration 221 with a length over at least 20 .mu.s before
starting data transmission.
[0060] If it is determined as a result of CCA that the unlicensed
band is not in use by another device, the transmitter may perform
transmission as denoted by reference number 224. Otherwise if it is
determined that the unlicensed band is in use by another device,
the base station or terminal in the LBE mode may perform additional
CCA. This additional CCA is referred to as extended CCA (ECCA) 223.
The ECCA consists of N CCAs, and N is a random number selected in
the range of [1, q] where q is a given number.
[0061] If it is determined as a result of ECCA that the unlicensed
band is not in use by another device, the transmitter may perform
transmission as denoted by reference number 224. Here, the time
duration in which the base station or terminal in the LBE mode
performs data transmission is referred to as channel occupancy
duration 225. The channel occupancy duration 225 lasts for up to
(13/32*q) ms and is followed by an idle duration 227 during which
the transmitter stays in the idle state 226 without data
transmission.
[0062] In the present invention, the base station may operate in
the LBE mode for downlink transmission, and the terminal may
operate in one of the FBE and LBE modes for uplink
transmission.
[0063] FIG. 3A is a diagram illustrating configurations of a TDD
frame according to an embodiment of the present invention.
[0064] In reference to FIG. 3A, the base station may detect an idle
channel during the first CCA duration 311 in the TTD frame 310. In
this embodiment, the TDD frame 310 includes consecutive downlink
subframes 312 in which the base station may perform downlink
transmission. That is, all downlink subframes are arranged
consecutively in the TDD frame 310. Here, the number of subframes
for use in downlink transmission may vary depending on the amount
of data to transmit. The base station may determine configuration
on the subframes including the consecutive downlink subframe in a
predetermined time period according to the data amount to transmit
and send the configuration information to the terminal.
[0065] The drawing depicts the TDD frame 310 with 6 downlink
subframes designated for downlink data transmission. In this case,
the base station may transmit the subframes configuration
information to the terminal. Also, the base station may transmit
downlink data for 6 ms because the duration of one subframe is 1
ms.
[0066] The TDD frame 310 may include a special subframe 313
following the consecutive downlink subframes 312 and consecutive
uplink subframes 314 following the special subframe 313.
[0067] The special subframe may include an idle duration defined in
the regulation. The other part of the special subframe may be used
by the base station or terminal for data or control signal
transmission.
[0068] In the TDD frame 310, the subframe carrying an initial
signal may be assigned subframe index 0. It may also be possible to
assign subframe index 0 to the subframe carrying the first data
following the initial signal. However, the subframe index
determination is not limited thereto.
[0069] In the drawing, the TDD frame 320 has a frame structure for
use in case where no idle channel is detected in the first CCA
duration 321.
[0070] If no idle channel is detected as a result of CCA in the
first CCA duration 321 of the TDD frame 320, the base station may
perform eCCA 323 in the next subframe, i.e., subframe 0 322. Here,
the time duration for performing the eCCA may be referred to as
eCCA duration. The eCCA duration may also be called channel
occupancy check duration.
[0071] If it is determined that the channel is in the idle state as
a result of eCCA 323 in subframe 0 322, the base station may
transmit downlink signals during the consecutive downlink subframes
326 starting from the next subframe, i.e., subframe 1 324.
[0072] However, the channel may be in use by another channel during
the duration 325 between the time point of detecting the idle state
of the channel and the time point of beginning the next subframe.
For this duration, the base station may transmit the initial signal
to occupy the channel.
[0073] The TDD frame 320 may also include a special subframe 327
following the consecutive downlink subframes 326 and uplink
subframes 328 following the special subframe 327.
[0074] In uplink, the terminal performing uplink transmission may
be changed every uplink subframe. The terminal may receive the
information on uplink subframes for receiving downlink data. The
terminal performs CCA or eCCA, to check whether the channel is
preoccupied, for uplink transmission at the allocated subframes. If
it is determined as a result of CCA or eCCA that the channel is in
the idle state, the terminal may transmit uplink data in the
corresponding subframes. Otherwise, if it is determined that the
channel is in an occupied state, the terminal may not transmit
uplink data in the corresponding subframes. The channel occupancy
time of the terminal for uplink data transmission may be 1 ms,
equal to the length of one subframe, or a multiple of 1 ms.
[0075] The terminal may perform CCA during the CCA duration 329
included in an uplink subframe, and the CCA duration 329 may
consist of the last one or n symbols of the uplink subframe.
Accordingly, there may be no signal transmission between the
terminal and the base station during the last 1 or n symbols of the
uplink subframe.
[0076] In the case of the terminal allocated the first uplink
subframe 329, i.e., subframe 7, of the TDD frame 320, the CCA or
eCCA may be performed in the downlink subframe or the special
subframe right before the first uplink subframe 329.
[0077] However, the position and length of the duration for CCA or
eCCA may be changed in the uplink subframes. A detailed description
thereof is made with reference to FIG. 3B.
[0078] FIG. 3B is a diagram illustrating configurations of a TDD
frame according to another embodiment of the present invention.
[0079] In reference to FIG. 3B, the TDD frames 330 and 340 are
characterized in that the CCA duration is changed in position and
sized in the uplink subframes.
[0080] In the case of the TDD frames 310 and 320, the CCA duration
consists of the last one or n symbols of the previous subframe.
Meanwhile, the CCA duration of the TDD from 330 consists of the
first 1 or n symbols of the subframe.
[0081] Accordingly, the base station may perform CCA during the CCA
duration 332 designated at the beginning of downlink subframe 0 331
of the TDD frame 330 and, if it is determined as a result of CCA
that the channel is not idle, then perform eCCA immediately.
[0082] The terminal may also perform CCA or eCCA during first 1 or
n symbols of each uplink subframe for uplink transmission.
Accordingly, there may be no signal transmission between the
terminal and the base station during the first 1 or n symbols of
the uplink subframe.
[0083] Meanwhile, the TDD configuration information related to the
TDD frame structure such as a start time point and number of
consecutive downlink subframes, a position of the special subframe,
a start time and number of consecutive uplink subframes, and CCA
and ECCA durations of downlink and uplink subframes may be changed
according to the data amount to be transmitted by the base station
and terminals.
[0084] The TDD frame 340 is different in that the number of
consecutive downlink subframes, the number of consecutive uplink
subframes, and the CCA durations are changed.
[0085] If the amount of data to transmit is small, the number of
consecutive downlink subframes may be decreased in the TDD frame
340. The TDD frame 340 includes 5 consecutive downlink subframes
while the TDD frame 330 includes 6 consecutive downlink
subframes.
[0086] The number of CCA durations may also be changed. In the case
that a terminal transmits uplink data through an unlicensed band
channel based on CCA, it may use two or more uplink subframes for
data transmission according to the data amount to transmit. In
reference to TDD frame 340, the terminal may perform CCA at an
interval of two subframes in uplink. However, the base station may
allocates uplink subframes to the terminal dynamically in number
according to the data amount to be transmitted by each terminal and
thus the interval of subframes for CCA may be dynamically
changed.
[0087] In the case of the LAA system, however, the base station
occupies the channel for a time duration that is sufficient to
transmit data as described above, and it is not necessary to
consider the fixed LTE frame length of 10 ms in configuring the TDD
frame.
[0088] The TDD frame 350 is characterized in that the number of
subframes is dynamically changed according to the data amount to be
transmitted. In the TDD frame 350, the number of consecutive
downlink subframes and the number of consecutive uplink subframes
may be changed and, as a consequence, the frame length may be
changed.
[0089] In detail, the TDD frame 350 may include 3 consecutive
downlink subframes and 2 consecutive uplink subframes that appear
sequentially after eCCA. In this case, the frame length becomes 7
ms shorter than the LTE frame length of 10 ms.
[0090] As described above, the TDD frame structured according to
the present invention may include consecutive downlink subframes,
special subframes, and consecutive uplink subframes. The TDD frame
proposed in the present invention may be configured such that all
downlink subframes are arranged consecutively and all uplink
subframes are arranged consecutively. The positions of the
consecutive downlink subframes, the consecutive uplink subframes,
and special subframes may be changed.
[0091] It may also be possible that the frame is configured to have
only the consecutive downlink subframes or only the consecutive
uplink subframes.
[0092] If the base station transmits the TDD frame configuration
information to a terminal at the current subframe or a subframe
before n subframes, the terminal may check the downlink/uplink
subframe configurations at the current subframe or a subframe after
m subframes. The terminal may receive a downlink control channel
(PDCCH) at the downlink subframes for performing Radio Resource
Management (RRM) measurement or CSI measurement based thereon. The
terminal may also determine one of the RRM management result and
CSI measurement result for a bundle of the consecutive subframes.
The base station may configure uplink subframes to the terminal to
receive a Physical Uplink Control Channel (PUCCH) or a Sounding
Reference Signal (SRS) and perform measurement thereon.
[0093] In order to apply the TDD frame structure proposed in the
present invention to an LAA system, the base station may transmit
the TDD configuration information to notify the terminal of the TDD
frame structure. The TDD configuration information may include at
least one of the informations listed in Table 1.
TABLE-US-00001 TABLE 1 Channel occupancy start time point, channel
occupancy end time point, residual channel occupancy time, frame
length, frame start time point, frame end time point, downlink
duration length, downlink duration start time point, downlink
duration end time point, residual downlink duration length, uplink
duration length, uplink duration start time point, uplink duration
end time point, residual uplink duration length, CCA or ECCA
duration of base station in downlink duration, CCA or ECCA duration
of terminal in uplink duration, position of special subframe,
presence/absence of partial subframe as part of total channel
occupancy duration, and whether each subframe is an ordinary 1 ms
subframe or a partial subframe shorter than 1 ms, etc.
[0094] Among the above information, the channel occupancy end time
point, frame end time point, downlink duration end time point, and
uplink duration end point may be notified to the terminal by
transmitting the corresponding time points explicitly or using the
special subframe structure specified in LTE. As described above, an
LTE special subframe consists of a DwPTS, an UpPTS, and a GP, which
are configured as shown in Table 2.
TABLE-US-00002 TABLE 2 3GPP DwPTS UpPTS Number of slots/subframe
Configuration release (Ts) (Ts) Dw GP Up 0 8 6592 2192 3 10 1 1 8
19760 2192 9 4 1 2 8 21952 2192 10 3 1 3 8 24144 2192 11 2 1 4 8
26336 2192 12 1 1 5 8 6592 4384 3 9 2 6 8 19760 4384 9 3 2 7 8
21952 4384 10 2 2 8 8 24144 4384 11 1 2 9 11 13168 4384 6 6 2
[0095] The base station may notify the terminal of the end time
information as follows.
[0096] If the base station notifies the terminal that the n.sup.th
subframe is the last downlink subframe and has the special subframe
configuration 0, the terminal assumes that the end time point of
the third symbol of the n.sup.th subframe is the downlink end time
point.
[0097] If the base station notifies the terminal that the n.sup.th
subframe is the last downlink subframe and has the special subframe
configuration 9, the terminal assumes that the end time point of
the 6.sup.th symbol of the n.sup.th subframe is the downlink end
time point.
[0098] As described above, the information such as the start and
end time points and number of consecutive downlink subframes, the
position of the special subframe, the start and end time points and
number of consecutive downlink subframes, and the CCA duration may
be changed according to the data amount to be transmitted by the
base station and terminal at every transmission. The TDD
configuration information may be changed at every CCA of the base
station or every subframe and, as a consequence, the base station
may transmit the changed TDD configuration information to the
terminal through PDCCH.
[0099] The base station may use at least one of the following
methods for transmitting the TDD configuration information.
[0100] If the base station is performing CCA or eCCA for a
secondary component carrier (SCell) operating in the unlicensed
band, it may transmit to the terminal the TDD configuration
information through a control channel of the primary component
carrier (PCell) operating in the licensed band. Here, the control
channel may include the information on Physical Downlink Control
Channel (PDCCH), System Information Block (SIB), Radio Resource
Control (RRC) configuration, and RRC reconfiguration. For example,
the base station may transmit to the terminal the information as
shown in Table 3 using a new element of the Downlink Control
Indicator (DCI) on PDCCH.
TABLE-US-00003 TABLE 3 Format 0 (example, other formats can be used
for the same purpose) Field name Length Comment Flag for
format0/format1A 1 differentiation Hopping flag 1 N_ULhop 1 (1.4
MHz) Applicable only when 1 (3 MHz) Hopping flag is set 1 (5 MHz) 2
(10 MHz) 2 (15 MHz) 2 (20 MHz) Resource block assignment 5 (1.4
MHz) 7 (3 MHz) 7 (5 MHz) 11 (10 MHz) 12 (15 MHz) 13 (20 MHz) MCS
and RV 5 NDI (New Data Indicator) 1 TPC for PUSCH 2 Cyclic shift
for DM RS 3 UL index (TDD only) 2 This field is present only for
TDD operation with uplink-downlink configuration 0 Downlink
Assignment 2 Only for TDD Index (DAI) Operation with uplink-
downlink configurations 1- 6 CQI request (1 bit) 1 LAA information
(newly N bits At least one of the elements added element) listed in
Table 1 can be transmitted from the base station to the terminal in
this way.
[0101] If the base station performs CCA or eCCA in the SCell
operating in the unlicensed band to occupy the channel, it may
transmit the TDD configuration information to the terminal using a
control channel (e.g., PDCCH, SIB, RRC configuration, and RRC
reconfiguration) of the SCell.
[0102] Also, if the base station performs CCA or eCCA in the SCell
operating in the unlicensed band to occupy the channel, it may
transmit the TDD configuration information using the initial
signal.
[0103] The base station may transmit to the terminal the TDD
configuration information through the PCell and, if necessary,
through the SCell. The terminal may combine or overwrite the
configuration information received through the SCell with or on the
configuration information received through the PCell.
[0104] As an example of the method for combining the configuration
information received through the PCell and the configuration
information received through the SCell, the terminal may be
configured with the channel occupancy start time point for the
target carrier received along with the cross-carrier scheduling
command through the downlink control channel of the PCell and then
configured with the channel occupancy end time point received
through the downlink control channel of the SCell in the course of
the downlink operation for the SCell on the target carrier. The
terminal may determine the downlink subframes of the SCell in
consideration of both the channel occupancy start time point
received through the PCell and the channel occupancy end time point
received through the SCell.
[0105] As an example of the method for overwriting the
configuration information received through the SCell on the
configuration received through the PCell, the terminal may be
configured with the channel occupancy start and end time points for
the target carrier received along with the cross carrier scheduling
command through the downlink control channel of the PCell and then
configured with the channel occupancy end time point (or residual
channel occupancy time) received through the downlink control
channel of the SCell in the course of performing downlink operation
for the SCell on the target carrier. The terminal may overwrite or
correct the channel occupancy end time point received through the
PCell with the channel occupancy end time point (or residual
channel occupancy time) received through the SCell. The terminal
may determine the downlink subframe of the SCell in consideration
of both the channel occupancy start time point received from the
PCell or the overwritten or corrected channel occupancy end time
point.
[0106] FIG. 4 is a diagram illustrating a method for performing CCA
on different types of channel according to an embodiment of the
present invention.
[0107] In order to use an unlicensed band, the base station has to
determine whether the unlicensed band is in use by another device
in the LAA system. Various parameters can be used for determining
whether an unlicensed band channel is occupied by another device
(or for performing CCA) and these parameters may be referred to as
channel occupancy parameters. The channel occupancy parameters may
include at least one of a CCA start time, a CCA duration, a CCA
threshold, an idle period, an ECCA duration, and a channel
occupancy time.
[0108] Meanwhile, a Wi-Fi device operating in an unlicensed band
such as an LAA unlicensed band also has to perform CCA and, in the
case of Wi-Fi, different channel occupancy parameters are used for
different types of traffic. For example, IEEE 802.11e defines
Enhanced Distributed Channel Access (EDCA) as a channel occupancy
parameter (hereinafter, interchangeable referred to as CCA
parameter, or Listen Before Talk (LBT) parameter) as shown in Table
4.
TABLE-US-00004 TABLE 4 Minimum Maximum contention window contention
window Max size (CWmin) size (CWmax) TXOP Background 15 1023 Best
effort 15 1023 3.008 ms Video 7 15 1.504 ms Voice 3 7 Legacy 15
1023
[0109] In reference to FIG. 4, the primary channel 410 and the
secondary channel 420 are discriminated by function. The channels
discriminated by function may mean the channels transmitting
different types of traffic or packets. As described above, since
the Wi-Fi system uses traffic-specific channel occupancy
parameters, different LBT parameters may be used for different
types of channel in a multi-channel operation.
[0110] For example, an Access Point (AP) or a Station (STA) may
perform eCCA during a DIFS period or a random back-off period on
the primary channel 410. Meanwhile, the AP or STA may perform CCA
during a PIFS on the secondary channel 420 to determine whether it
is possible to occupy the channel.
[0111] Since the Wi-Fi system uses the same LBT parameter on
different physical channels, the AP or STA have no preference for
any specific channel. Accordingly, the AP or STA may observe the
average channel occupancy time per channel to select the channel
with the least average channel occupancy time.
[0112] By selecting a channel in this way, the types of traffic may
be randomized on the respective channel; however, in the case that
the channel allocation to the terminal is performed in a
centralized manner as with being performed by an base station of an
LTE system, it may be possible to improve the channel management
efficiency and a detailed description thereof is made
hereinafter.
[0113] FIG. 5 is a diagram illustrating a situation where different
types of traffic are carried on different channels in an unlicensed
band to which an embodiment of the present invention is
applicable.
[0114] FIG. 5 exemplifies a situation where channel 1 510 and
channel 2 520 carry voice packets, channel 3 530 carries data
packets, and channel 4 540 carries voice, data, and video
packets.
[0115] The voice packets 511 and 521 transmitted on the channel 1
510 and channel 2 520 may be relatively small in size in comparison
with the data packet or video packet. The voice packet occurrence
interval may be changed according to the number of APs, and the
voice packets may be transmitted at a relatively short interval in
comparison with the data or video packet.
[0116] Meanwhile, the data packet 531 transmitted on channel 3 530
and the data and video packets 541 and 542 transmitted on channel 4
540 may be relatively large in size in comparison with the voice
packet. The data and video packets may be transmitted at a
relatively long interval in comparison with the voice packet.
[0117] FIG. 6A is a diagram illustrating a situation of
transmitting LAA voice packets in an unlicensed band to which an
embodiment of the present invention is applicable.
[0118] Similar to the situation of FIG. 5, in the situation of FIG.
6A, channel 1 610 and channel 2 620 carry Wi-Fi voice packets,
channel 3 630 carries Wi-Fi data packets, and channel 4 640 carries
Wi-Fi video, data, and voice packets.
[0119] In the case of attempting LAA voice packet transmission on
channel 1 610 and channel 2 620 carrying the Wi-Fi voice packets,
the base station can transmit the LAA voice packets 611 and 621 in
the time durations with no Wi-Fi voice packet although the channel
load is high.
[0120] Meanwhile, in the case of attempting LAA voice packet
transmission on channel 3 630 and channel 4 640 carrying data
packets, the voice packets transmitted by the base station and the
Wi-Fi data packets are likely to collide in spite of low channel
load because the Wi-Fi data packet is large in size. For example,
the LAA voice packets 631 and 632 transmitted on channel 3 630 may
collide with the data packet 633. Also, the LAA voice packets 641
and 642 transmitted on channel 4 640 may collide with the data
packet 643 and the video packet 644.
[0121] Such collision between the Wi-Fi and LAA packets may
decrease the data throughputs of both the Wi-Fi and LAA
systems.
[0122] FIG. 6B is a diagram illustrating a situation of
transmitting LAA data packets in an unlicensed band to which an
embodiment of the present invention is applicable.
[0123] Channel 1 650 and channel 2 660 carry Wi-Fi voice packets,
channel 3 670 carries Wi-Fi data packets, and channel 4 680 carries
Wi-Fi video, data, and voice packets in a Wi-Fi network.
[0124] It is assumed that an LAA base station transmits data
packets on channel 1 650 and channel 2 660 carrying the Wi-Fi voice
packets. In this case, the LAA data packets are likely to collide
with the Wi-Fi voice packets if the voice packets are transmitted
frequently at a short interval in spite of low channel load. For
example, the LAA data packet 651 transmitted on channel 1 650 may
collide with the Wi-Fi voice packets 652.
[0125] Also, the LAA data packet 681 transmitted on channel 4 680
may collide with the Wi-Fi data packet 682.
[0126] However, if the Wi-Fi data packets are transmitted at a long
interval, the LAA base station may transmit the LAA data packet in
the time durations with no Wi-Fi data packets as shown in the case
where the LAA base station transmits the data packets on channel 3
670 carrying the Wi-Fi data packets.
[0127] If the channel occupancy time is short and if the types of
traffic carried on the channel are similar, it may be possible to
use the channel more efficiently. For this reason, the present
invention proposes a method for an LAA base station or terminal to
check the channel occupancy behaviors of the devices operating on
the channels and use LBT parameters suitable for the respective
channels.
[0128] FIG. 7A is a flowchart illustrating a LBT parameter
determination procedure according to an embodiment of the present
invention.
[0129] In reference to FIG. 7A, the base station may check channel
occupancy status per channel at step S710. The base station may
scan channels available in an unlicensed band during a
predetermined period and observe the channel occupancy status.
[0130] Next, the base station determines channel state information
for determining LBT parameters at step S720 based on the channel
occupancy status.
[0131] The channel state information may include at least one of
the parameters listed in Table 5.
TABLE-US-00005 TABLE 5 Average channel occupancy time of other
devices, number of transitions from channel occupancy state
(hereinafter, term "busy state" is interchangeably used) to channel
non-occupancy state(term "idle state" is interchangeably used),
number of transitions from idle state to busy state, average time
of channel occupancy durations, total time of channel occupancy
durations, average time of idle durations, total time of idle
durations, standard deviation of occupancy durations, and standard
deviation of idle durations
[0132] The channel state information is described in detail with
reference to FIG. 8.
[0133] FIG. 8 is a diagram for explaining channel state information
checked by an base station based on channel occupancy status
according to an embodiment of the present invention.
[0134] In reference to FIG. 8, a time duration for the base station
to check the channel state of the unlicensed band may be referred
to as observation period 810. The base station may perform
observation during the observation period 810 to determine whether
the unlicensed band is occupied and generate channel state
information based on the determination result.
[0135] The base station may check occupancy durations (hereinafter,
interchangeably referred to as busy durations) and non-occupancy
durations (interchangeably referred to as "idle durations").
[0136] The base station may measure received signal strength during
a predetermined period and, if the received signal strength is
greater than a predetermined value, may determine the corresponding
duration as the occupancy duration. Otherwise, if the received
signal strength is equal to or less than the predetermine value,
the base station may determine the corresponding duration as the
idle duration.
[0137] In FIG. 8, the base station may check three occupancy
durations 820 and three idle durations 830 in the unlicensed band.
The base station may also check the occupancy durations of B1 821,
B2 822, and B3 823. The base station may calculate the average
occupancy time of the occupancy durations and the standard
deviation 824 of the occupancy durations B1, B2, and B3.
[0138] The base station may also check the idle durations of I1
831, I2 832, and I3 833. The base station may calculate the average
time of the idle durations I1, I2, and I3 and standard deviation
834 of the average value.
[0139] The base station may also determine a channel occupancy
ratio 840 using the length of the observation period, the total
occupancy time of the occupancy durations, and the total idle time
of the idle durations.
[0140] The base station may also determine the number of
transitions 850 between the occupancy duration and the idle
duration during the observation period 810. The base station may
determine the number of transmissions 850 based on the number of
occupancy durations and the number of idle durations during the
observation period 810.
[0141] The base station may determine LBT parameters based on the
number of transitions between the occupancy duration and the idle
duration. A detailed description thereof is made later.
[0142] The base station may also determine a number of idle
slots.
[0143] The term "slot" means a time unit for use in determining an
idle state or an occupancy time. For example, one slot may have the
length of 9 us. The base station may make a decision on idle state
or occupancy state by slot and determine numbers of idle slots and
occupancy slots.
[0144] For example, the base station may determine the number of
idle slots by dividing the total length of the idle time by the
length of one slot. The base station may also determine the ratio
of the idle slots by dividing the total length of the idle time by
the length of the observation period. The base station may also
determine the radio between the number of idle slots and the number
of occupancy slots (busy slots) in the observation period. For
example, the base station may determine the ratio between the idle
slots and the occupancy slots (busy slots) by dividing the total
length of the idle time by the total length of the occupancy
time.
[0145] The base station may determine the LBT parameters based on
at least one of the number of idle slots, the ratio of the idle
slots, and the ratio between the idle slots and the occupancy
slots.
[0146] Although the description is directed to the case where the
base station checks the channel state and determines the channel
state information for convenience of explanation, the present
invention is not limited thereto. That is, the terminal may check
the channel state and determine the channel state information, and
the base station may determine LBT parameters based on the channel
state information determined by the terminal.
[0147] Returning to FIG. 7A, after determining the channel state
information, the base station may determine LBT parameters per
channel based on channel-related parameters at step S730. In the
case that the terminal checks the channel state, the base station
may receive the channel state information from the terminal and
determines the LBT parameters based on the received channel state
information.
[0148] The LBT parameters may include at least one of the
parameters listed in Table 6.
TABLE-US-00006 TABLE 6 CCA start time, CCA duration, CCA threshold,
channel occupancy time, idle duration, ECCA duration
[0149] Here, the ECCA duration may be referred to as a channel
occupancy check duration. The ECCA duration may be determined by a
contention window size of the LAA system, and the base station may
calculate the contention window size based on the number of
transitions from the occupancy state to the idle state, the number
of idle slots, or the ratio between the number of idle slots and
the number of occupancy slots, as part of the channel state
information to determine the ECCA duration. The LBT parameters may
be determined using various method and algorithms, and detailed
descriptions thereof are made later.
[0150] Next, the base station may transmit the per-channel LBT
parameters to the terminal at step S740.
[0151] The base station may transmit the LBT parameters to the
terminal through a PCell operating in the licensed band. In detail,
the base station may transmit the LBT parameters using a PDCCH, an
SIB, an RRC connection configuration message, or an RRC connection
reconfiguration message of the PCell operating on the licensed
band.
[0152] FIG. 7B is a flowchart illustrating a procedure for
determining LBT parameters based on a channel state according to an
embodiment of the present invention.
[0153] In reference to FIG. 7B, the base station may check the
channel state of the unlicensed band during an observation period
at step S751 and determine channel state information at step S752.
Since these steps are similar to steps S710 and S720 of FIG. 7A,
detailed descriptions thereof are omitted herein.
[0154] Next, the base station may perform a channel state
information comparison at step S753. The base station may compare
the channel state information determined during the current
observation period and the channel state information determined
during the previous observation period.
[0155] The base station may select at least one of the number of
transitions from the occupancy duration to the idle duration, the
average occupancy time of the occupancy durations, and the total
occupancy time of the occupancy durations included in the channel
state information for use in the comparison. The base station may
compare the parameters of the current observation period and the
previous observation period.
[0156] As a comparison result, if the channel state information of
the current observation period is less than the channel state
information of the previous observation period, the base station
may initialize the contention window size to the least value at
step S755.
[0157] Otherwise, if the channel state information of the current
observation period is equal to or greater than the channel state
information of the previous observation period, the base station
may double the contention window size at step S756.
[0158] That is, if it is determined that the channel state
information increases based on the comparison between two
successive observation periods, this may indicate an increase in
the number of users. In this situation, the base station may double
the contention window size to avoid collision of packets
transmitted on the same channel. Otherwise, if the parameter value
of the channel state information decreases, the base station may
initialize the contention window size.
[0159] Next, the base station may select a random number in the
determined contention window size at step S757. Next, the base
station may perform channel occupancy assessment (LBT) for access
to the unlicensed band based on the selected random number at step
S758. In detail, if the base station succeeds in CCA as many times
as the selected number, it can access the unlicensed band.
[0160] FIG. 7C is a flowchart illustrating a procedure for
determining LBT parameters based on a channel state according to
another embodiment of the present invention.
[0161] In reference to FIG. 7C, the base station at step S761 may
check the channel state of the unlicensed band during an
observation period and determine channel state information at step
S762. Since these steps are similar to steps S710 and S720 of FIG.
7A, detailed descriptions thereof are omitted herein.
[0162] Next, the base station may perform a channel state
information comparison at step S763. The base station may compare
the channel state information determined during the current
observation period and the channel state information determined
during the previous observation period.
[0163] The base station may select at least one of the number of
transitions from the occupancy duration to the idle duration, the
average occupancy time of the occupancy durations, and the total
occupancy time of the occupancy durations included in the channel
state information for use in the comparison. The base station at
step S764 may compare the parameters of the current observation
period and the previous observation period.
[0164] As a comparison result, at step S764 if the channel state
information of the current observation period is less than the
channel state information of the previous observation period, the
base station may determine a new contention window size by
multiplying the contention window size by a predetermined first
constant p at step S765. At this time, the first constant value p
may be greater than 0 and less than 1.
[0165] Otherwise, if the channel state information of the current
observation period is equal to or greater than the channel state
information of the previous observation period, the base station
may determine a new window size by multiplying the contention
window size by a predetermined second constant value q at step
S766. The second constant value q may be greater than 0 and less
than 1.
[0166] Here, p and q may be determined according to a contention
window size decrement/increment rate. Also, p and q may be set to
values fulfilling the conditions of 0<p<1 and q>1.
[0167] Next, the base station may select a random number in the
determined contention window size at step S767. Next, the base
station may perform channel occupancy assessment (LBT) for access
to the unlicensed band based on the selected random number at step
S768. In detail, if the base station succeeds in CCA as many times
as the selected number, it can access the unlicensed band.
[0168] FIG. 7D is a flowchart illustrating a procedure for
determining LBT parameters based on a channel state according to
still another embodiment of the present invention.
[0169] In reference to FIG. 7D, the base station may check the
channel state of the unlicensed band during an observation period
at step S771, and determine channel state information at step S772.
Since these steps are similar to steps S710 and S720 of FIG. 7A,
detailed descriptions thereof are omitted herein.
[0170] Next, the base station determines a contention window size
based on a pre-stored mapping table and the channel state
information at step S773. Table 7 is an example of the pre-stored
mapping table.
TABLE-US-00007 TABLE 7 channel state information (X) Contention
window X < N.sub.0 16 N0 <= X < N1 32 N1 <= X < N2
64 N2 <= X < N3 128 N3 <= X < N4 256 N4 <= X < N5
512 N5 <= X 1024
[0171] The base station may select at least one of the number of
transitions from the occupancy duration to the idle duration, the
average occupancy time of the occupancy durations, and the total
occupancy time of the occupancy durations as the channel state
information for use in determining the contention window size.
[0172] The base station may determine the contention window size
using the channel state information of the current observation
period and the mapping table.
[0173] Next, the base station may select a random number in the
determined contention window size at step S774. Next, the base
station may perform channel occupancy assessment (LBT) for access
to the unlicensed band based on the selected number. In detail, if
the base station succeeds in CCA as many times as the selected
number step S775, it can access the unlicensed band.
[0174] Meanwhile, in an environment where the AP and STAs generate
different types of traffic on a certain channel of the unlicensed
band, the irregular channel occupancy pattern makes it difficult to
determine the LBT parameters. For this reason, the present
invention proposes a method for selecting a channel, the method
being described hereinafter.
[0175] FIG. 9 is a flowchart illustrating a procedure for selecting
a channel to which the LBT parameter determined based on channel
states is applied according to an embodiment of the present
invention.
[0176] The base station may check the average occupancy time of a
channel occupied by other devices at step S910. The average channel
occupancy time of other devices may be determined based on the
unlicensed band channel state checked by the base station or the
terminal.
[0177] The base station may check whether the channel is a low-load
channel or a high-load channel using the average channel occupancy
time at step S920. If the average occupancy time is less than a
predetermined value, the base station may determine the channel as
a low-load channel.
[0178] Next, the base station may determine whether a channel is a
short packet channel or a long packet channel at step S930. In
detail, the base station may check the packet lengths on the
respective channels based on the number of transitions from the
occupancy duration to the idle duration, the number of transitions
from the idle state to the occupancy state, the average time of
occupancy durations, and average time of idle durations included in
the channel state information.
[0179] For example, the base station may determine that the packet
transmitted on a channel with a short average occupancy time is
short in length. That is, the base station may determine the
channel on which the average occupancy time value is less than a
predetermined value as a short packet channel. It may also be
possible to determine the channel on which the number of
transitions from the occupancy state to the idle state is less than
a predetermined value and the average occupancy time is shorter
than a predetermined length as the short packet channel. The above
packet length determination method is only an exemplary embodiment,
and the present invention is not limited thereby.
[0180] Next, the base station may determine at step S940 whether it
is possible to apply the LBT parameters determined based on the
channel condition to the channel. That is, the base station may
determine whether the information acquired at the previous step is
valid. This is because an irregular channel occupancy pattern makes
it difficult for the base station to determine and apply LBT
parameters according to the channel condition. Here, the base
station may use the standard deviations of the occupancy durations
and idle durations.
[0181] If the standard deviation of the occupancy durations is
large, this may mean that the information mismatch between the
occupancy durations is large. If the standard deviation is large,
this means that the acquired information is uneven; thus, the base
station may determine that the information acquired based on the
average of the occupancy durations is invalid. In this case, the
base station may not use the LBT parameters determined based on the
channel condition in association with the channel with large
standard deviations of the occupancy durations and idle
durations.
[0182] Meanwhile, the base station may determine that the
information acquired on the channel with an occupancy or idle
duration standard deviation less than a predetermined value is
valid and thus that the LBT parameters are applicable.
[0183] If it is determined that the acquired information is valid,
the base station may apply the determined LBT parameters at step
S950. In detail, the base station may sort the channels into 4
groups and apply the LBT parameters to the respective channels.
[0184] FIG. 10 is a diagram illustrating a procedure for sorting
channels into four channel groups according to an embodiment of the
present invention.
[0185] In reference to FIG. 10, the four channel groups include the
first channel group 1010 characterized by large packet length and
high load, the second channel group 1020 characterized by small
packet length and high load, the third channel group 1030
characterized by large packet size and small load, and the fourth
channel group 1040 characterized by large packet size and high
load.
[0186] The base station may check occupancy states of available
unlicensed band channels and determine load states of each of the
channels based on the occupancy states at step S1010. For example,
the base station may determine the load states of the channels
using the average occupancy times and channel occupancy ratios of
each of the channels. Here, the base station may compare the
average occupancy times or channel occupancy ratios of the channels
to sort the channels into a high-load channel category and a
low-load channel category. That is, the base station may sort the
channels with an average occupancy time or occupancy ratio greater
than a predetermined value into a high-load channel.
[0187] Afterward, the base station may check packet lengths at step
S1020. The base station may determine the packet length per channel
based on the number of transitions between occupancy duration and
idle duration and average times of occupancy durations and idle
durations.
[0188] For example, the longer is the average time of the
occupation durations, the longer is the packet length. Accordingly,
if the average time of the occupancy durations is long, the base
station determines that the packet length is long.
[0189] Next, the base station may determine at step S1030 whether
the LBT parameters determined based on the channel condition are
valid. The base station checks the validity of the information
acquired on the channel using the standard deviations of the
occupancy durations and idle durations. If the standard deviation
is less than a predetermined value, the base station may validate
the validity of the information acquired on the channel and
determine and apply the LBT parameters. If it is determined that
the information acquired on the channel is valid, the base station
may sort the channel into one of the channel groups.
[0190] For example, base station may sort the channel with a high
load and short packet length into the first channel group.
[0191] After sorting the channels, the base station may apply the
LBT parameters according to the per-channel conditions.
[0192] FIG. 11 is a diagram illustrating a method for determining
LBT parameters per channel according to an embodiment of the
present invention.
[0193] FIG. 11 shows two methods for determining LBT parameter per
channel.
[0194] In the first method, the base station and the terminal store
at least one predetermined LBT parameter set, and the base station
transmits to the terminal an index of the LBT parameter set
determined per channel.
[0195] In this case, each LBT parameter set may include at least
one LBT parameter. For example, an LBT parameter set may include
CCA duration, ECCA duration, and CCA start time. The base station
and the terminal may store the index of the at least one parameter
set, and the base station may send the terminal the index of the
LBT parameter set currently in use.
[0196] In method 1 1110 of FIG. 11, a predetermined LBT parameter
set 1 1111 and a predetermined LBT parameter set 2 1112 may be
stored in the base station and the terminal. The base station may
determine to use the LBT parameters included in the LBT parameter
set 1 1111 for channel 1 1130 and channel N 1133 and then transmit
the index of the LBT parameter set 1 to the terminals operating on
channel 1 1130 and channel N 1133.
[0197] The base station may also determine to use the LBT
parameters included in the LBT parameter set 2 1112 for channel 2
1131 and channel 3 1132 and, in this case, transmit the index of
the LBT parameter set 2 to the terminals operating on the
corresponding channels.
[0198] In the second method, the base station determines LBT
parameters per channel and notifies the terminal of the parameters
explicitly.
[0199] In method 2 1120 of FIG. 11 the base station may check
channel state per channel, determine LBT parameters based on the
channel state, and transmit the parameters to the terminal.
[0200] The steps of checking channel state and determining LBT
parameters based on the channel states are identical with those of
FIG. 7.
[0201] After determining the LBT parameters to be applied per
channel, the base station may transmit the LBT parameters to the
terminal using an SIB, a PDCCH, or an RRC configuration message. A
detailed description thereof is made with reference to FIG. 12.
[0202] FIG. 12 is a signal flow diagram illustrating a procedure
for transmitting LBT parameters to a terminal according to an
embodiment of the present invention.
[0203] In reference to FIG. 12, an LAA base station may use a
primary carrier (PCell) in a licensed band and a secondary carrier
(SCell) in an unlicensed band. In this case, the base station may
check the channel state of the unlicensed band at step S1210. Also,
the terminal may check the channel state of the unlicensed band at
step S1210. The channel state checking step of the terminal is
optional.
[0204] In the case that the terminal checks the channel state, the
base station may receive a channel state measurement report
associated with the unlicensed band at step S1220. The measurement
report may include channel state information.
[0205] If the measurement report is received from the terminal, the
base station may determine LBT parameters based on the base
station-measured channel state and the measurement report.
[0206] The base station may determine the LBT parameters based on
the channel state measurement report received from the terminal and
the occupancy parameters determined through its channel observation
and analysis. For example, the base station may determine the ECCA
duration by adjusting the contention window size based on the
channel state.
[0207] After determining the LBT parameters, the base station may
transmit the LBT parameters to the terminal at step S1230. In this
case, the base station may transmit the LBT parameters using at
least one of an SIB, a PDCCH, and an RRC configuration
information.
[0208] The base station may also transmit an index of an LBT
parameter set or LBT parameter information using at least one of
the SIB, PDCCH, and RRC configuration information.
[0209] FIG. 13 is a block diagram illustrating a configuration of
an base station according to an embodiment of the present
invention.
[0210] In reference to FIG. 13, the base station may include a
transceiver 1310, a controller 1320, and a memory 1330.
[0211] The transceiver 1310 may communicate with a network
entity.
[0212] According to an embodiment of the present invention, the
transceiver 1310 may transmit TDD configuration information of a
TDD frame to a terminal. The transceiver 1310 may also transmit
downlink data to the terminal and receive uplink data from the
terminal.
[0213] According to an embodiment of the present invention, the
transceiver 1310 may receive a channel state measurement report
from the terminal. The transceiver 1310 may also transmit to the
terminal the LBT parameters determined based on the channel
state.
[0214] According to an embodiment of the present invention, the
controller 1320 may perform CCA during an initial CCA duration to
determine whether an unlicensed band channel is occupied. If it is
determined that the channel is occupied, the controller 1320 may
perform eCCA during the next CCA duration. If it is determined as a
result of CCA or eCCA that the unlicensed band channel is idle, the
base station may occupy the unlicensed band channel to transmit
downlink data. Here, a frame may be configured to have consecutive
downlink subframes. In this case, the base station may transmit
downlink data during the consecutive downlink subframes. Here, the
number of downlink subframes may be changed.
[0215] The controller 1320 may also perform CCA or eCCA during the
first one or n symbols of every subframe according to the
configuration of the TDD frame. The controller 1320 may also
perform CCA or eCCA during the last one or n symbols of every
subframe.
[0216] The base station may generate TDD configuration information
corresponding to the determined frame structure and transmit the
TDD configuration information to the terminal.
[0217] If the base station performs CCA or eCCA on a secondary
carrier (SCell) of the unlicensed band, the controller 1320 may
transmit the TDD configuration information to the terminal using
the control channel of the primary carrier (PCell). The control
channel of the PCell may include the information on PDCCH, SIB, RRC
configuration, and RRC reconfiguration.
[0218] If the base station occupies the channel through CCA and
eCCA in the SCell operating in the unlicensed band, the controller
1320 may transmit the TDD configuration information using a control
channel of the SCell such as PDCCH, SIB, RRC configuration, and RRC
reconfiguration of the SCell.
[0219] If the base station occupies the channel through CCA or eCCA
in the SCell operating in the unlicensed band, the controller 1320
may transmit the TDD configuration information to the terminal
using an initial signal transmitted by the base station.
[0220] According to an embodiment of the present invention, the
controller 1320 may check the channel state of the unlicensed band
and determine channel state information based thereon. The
controller 1320 may also determine LBT parameters based on the
channel state information. In this case, if the channel state
information value increases in comparison with the previous
observation period, the controller 1320 may increase the contention
window size and determine the LBT parameters. The controller 1320
may also perform a channel access procedure with the LBT parameters
to access the unlicensed band channel. The controller 1320 may also
transmit to the terminal at least one of an index of an LBT
parameter set and RRC configuration information using at least one
of an SIB, a PDCCH, and RRC configuration information.
[0221] Meanwhile, any irregular channel occupancy pattern makes it
difficult to apply the LBT parameters determined based on the
channel state. Accordingly, the controller 1320 may determine the
load state of the channel based on the channel occupancy time and
may determine per-channel packet length based on information such
as the number of transitions from occupancy state to idle state,
the number of transitions from idle state to occupancy state, the
average time of occupancy durations, and average time of idle
durations. Additionally, the controller 1320 may determine validity
of acquired information based on the standard deviation of each
occupancy duration, standard deviation of each idle duration and
may determine whether to apply the LBT parameter.
[0222] According to an embodiment of the present invention, the
memory 1330 may store the TDD configuration information related to
the TDD frame structure. The memory 1330 may also store CCA
parameters for performing CCA.
[0223] According to an embodiment of the present invention, the
memory 1330 may store LBT parameter sets including LBT parameters
and indices of the LBT parameter sets. The memory 1330 may also
store the channel state information generated based on the channel
state. The memory 1330 may also store the information related to
the channel state received from the terminal.
[0224] FIG. 14 is a block diagram illustrating a configuration of a
terminal according to an embodiment of the present invention.
[0225] In reference to FIG. 14, the terminal may include a
transceiver 1410, a controller 1420, and a memory 1430.
[0226] The transceiver 1410 may communicate with a network
entity.
[0227] According to an embodiment of the present invention, the
transceiver 1410 may receive TDD configuration information from an
base station. The transceiver 1410 may receive downlink data from
the base station and transmit uplink data to the base station.
[0228] According to an embodiment of the present invention, the
transceiver 1410 may transmit a channel state measurement report to
the base station. The controller 1410 may also receive LBT
parameters from the base station.
[0229] According to an embodiment of the present invention, the
controller 1420 may perform CCA during uplink subframes allocated
by the base station to determine whether the unlicensed band
channel is occupied. If it is determined that the channel is
occupied, the terminal may not transmit uplink data. Otherwise it
is determined that the channel is not occupied, the terminal may
transmit uplink data to the base station.
[0230] The controller 1420 may perform CCA or eCCA during the first
one or n symbols of the uplink subframe allocated by the base
station according to the TDD frame structure. The controller 1420
may also perform CCA or eCCA during the last one or n symbols of
the previous subframe.
[0231] If it is determined as a result of CCA performed by the base
station that the unlicensed band channel is in the idle state, the
controller 1420 may also control receiving data during consecutive
downlink subframes.
[0232] The controller 1420 may also control receiving the TDD
configuration information corresponding to the frame structure from
the base station.
[0233] According to an embodiment of the present invention, the
controller 1420 may check an unlicensed band channel state and
determine channel state information based thereon. The controller
1420 may also control transmitting the channel state information to
the base station. The channel state information may be used for
determining the LBT parameters.
[0234] The controller 1420 may also control receiving LBT parameter
information from the base station. The controller 1420 may also
control receiving an index of an LBT parameter set or LBT parameter
information through at least one of an SIB, a PDCCH, and RRC
configuration information.
[0235] According to an embodiment of the present invention, the
memory 1430 may store the TDD configuration information received
from the base station. The memory 1430 may also store the CCA
parameters for use in performing CCA.
[0236] According to an embodiment of the present invention, the
memory 1430 may store LBT parameter sets including LBT parameters
and indices of the LBT parameter sets.
[0237] The memory 1430 may also store the channel state information
generated based on the channel state.
[0238] Although the description has been made with reference to
particular embodiments, the present invention can be implemented
with various modifications without departing from the scope of the
present invention. Thus, the present invention is not limited to
the particular embodiments disclosed and will include the following
claims and their equivalents.
* * * * *